Over the weekend I tried to make the smallest possible opto theremin based on the common 555 chip. It uses one photocell and one 10uF capacitor. There is a switch embeded that inverts the Wave and Duty creating a different tone color of the square wave. At the bottom there is a 9volt connector. The headphone jack is soldered directly to the pin 3 of the output with a 8 ohm resistor to match the impedence. Everything is shrink wrapped with a hole cut for the opto resistor and fiilled with hot glue for durability. I will post audio files soon as well as a schematic once I find some free drafting software.